Method of increasing the productivity of oil wells



Feb. 12, 1952 E. v. WATTS EIAL 2,585,522

METHOD OF INCREASING THE PRODUCTIVITY OF OIL WELLS Filed March 8, 1947GAUGED PRODUCT/0N BARRELS ML. PER DAY GAUGED PRODUCT/0N, BARREL-S AGE/VT110050,. ML.PER DAV EUCLID V. WATTS BERT FOLQAJR.

y INVENTORS M W- ATTORNEY Patented Feb. 12, 1 9 52 astsszz W Mirrnoo OFINCREASING THE PRODUC- TIVITY OF OIL WELLS Euclid V. Watts, SouthPasadena, and Bert Folda,

' Jr., Los Angeles, Calif., assignors to Socony- Vacuum Oil Company,Incorporated, New York,

1 N. Y., a corporation of New York Application Mai-ch8 947, Serial No.733,282

' 2Claims. 1

This invention relates to the pumping of oil wells, and particularly tosteps by which the yield of heavy and viscous oilsmay be materiallyincreased.

It is well known that mostcrude petroleums, when in position in thesand, contain material amounts of dissolved hydrocarbon gas. When thepressure on the oil is reduced or released by passage through thesand'and the perforations into the casing, this gas passes out cfsolution in the form of extremely minute bubbles. If the oil is of lowviscosity, these bubbles rise rapidly through the oil column the'casihgand do not interfere with pumping operations. But in cases in which theoil is viscousand has a high surface tension the minute bubbles risevery slowly' by reason of the high viscosity and are prevented fromaggregating intolarger bubbles by the high surface tension, the resultbeing the formation ofaflne grained and very stable froth.

In the conventional reciprocating oil well pump,

located far below the earths surface, a standing available, for example?the control of plunger speeds; an increase in stroke length, by whichend clearance is reduced; increase in the pressure maintained on thecasing, and the use of gas anchors inwhich thefroth is separatedmechanically from the oil andis in part broken .down. All of theseexpedients are useful'under suitable conditions. but none has provenadequate to permit a gassy, heavy oil well to producethe vmaxi- 1 mumquantity of oil of which .it is inherently capable.

valve at the lower end of the pump barrel admits fluid during theupstroke offthe plunger; at whatever pressure may exist in the casing.During the ensuing down stroke a travelling valve in the plunger opensto permit the fluid trapped in the pump barrel to pass to the upper sideof the plunger, by which it is lifted through the tubing on the nextupstroke. 7

So long as the fluid entering below the plunger is wholly orsubstantially liquid, and therefore substantially incompressible, suchpumps will lift and discharge a volume of oil approximating theirdisplacement. But where the fluid entering the barrel is a highlycompressible mixture of oil and gas, the travelling valve does not openuntil the gas has been compressed sufiiciently to over-balance thepressureof the column of oil in the tubing and resting on the valve. I

In such cases the effective stroke of the pump is that portion of thetotal stroke measured from the point at which the travelling valve opensto the point at which stroke direction reverses, and in many instancesis only a small fraction of the whole. In extreme cases the quantit ofgas contained in the froth remaining in the clearance space at the endof the down stroke may be sufficient to fill the barrel during the upstroke at a pressure no greater than that existing below the standingvalve. In these cases the standing We have discovered that the abovedifficulties may be corrected and the production of frothy oil wellslargely increased by the introduction into the well of extremelyminuteamounts of the class of substances used as defoamants in lubricatingoils. Numerous metallo-organic substances are available for thatpurpose, but we prefer to use the dihydrocarbon silicates and siliconesdescribed in United States Patents 2,258,218 to'Rochow and 2,385,384 toMcGregor. The use of these substance in preventing lubricating oils fromfoaming is common practice and has been-highly successful. i

We have also discovered that destabilization of the froth and theconsequent more rapid separation of the ga act not merely to increasethe liftvalve does not open during the up stroke of the plunger, nofluid enters the barrel and the pump becomes gas-locked andnonfunctional.

Many partial remedies for these conditions are ing capacity of anygivenpump, but that they increase the actual productivity of the well bypermitting a lower liquid level to be carried in the casing and thusreducing the back pressure of the oil column against the producingformatlon.

The conditions existing in anoil well are quite different from thoseexisting in enclosures in which lubricating oils are used. In the latterthe foam is produced by strong agitation of the oil body and thefunction of the defoamant is rather .to prevent the formation of foamthan to break it after it has formed. The froth encounteredin an oilwell is generated in the sands adjacent the well bore. by release ofpressure and consequent evolution of part of the dissolved gas, andthefunction of the defoamant is to break foam already formed. a

The remarkable effectiveness of these agents in resolving crude oilfroth is illustrated by the results of the following experiment.Measured samples of froth were taken direct from the lead line of ,awell producing a very frothy crude of 14.6 A. P. I. gravity. Into thesesamples were stirred the minute quantities of dirnethyl silicone shownin the following table, in solution in diesel oil. The froth sampleswere stirred vigorously for one minute to disperse the defoamant throughthe froth and were then allowed to stand and the volume of the frothmeasured at the intervals shown in the table. After sixty minutesobservation the samples were allowed to stand until no gas remained inthe oil, the volume of oil being then measured. The difference betweenthe total volume of the sample at each observation time and the net oilvolume was assumed to be the volume of free gas present in the form offroth, and this quantity divided by the difi'erence between the originalvolume and the net oil volume represents the percentage of the originalgas remaining in the form of froth.

Table Parts per Million Added Deioamaut The benefits resulting from theuse of defoamants in frothy oil wells is even more strikinglyillustrated by the following field experiments, described below withreference to the production curves of the well shown in the two figuresof the attached drawing. The experiments were carried out in the samewell, at different times, under the following conditions:

Depth of well feet 2530 Pump set at do 2446 Gas anchor, 2 length do- 21Pump, diameter do 2 Pump strokes per minute, both experiments Length ofstroke, first experiment inches 24 Displacement, barrels per day, firstexperiment inches 125 Length of stroke, second experiment do 44Displacement, barrels per day, second experiment inches 300 Gravity ofoil A. P. I 14.6

In the first experiment, illustrated by the curves of Fig. 1, a quantityof dimethyl silicone ranging from 7 to 32 millilitres per twenty-fourhours was introduced into the well in the form of a solution in dieseloil at a concentration of 0.22%. The e iifeot of the first addition wasobservable the folylowing day in a sharp rise in the production curveand this increased productivity persisted for three days after theaddition of the agent was discontinued. During the entire period ofobservation, thirty-six days, the trend of productivity was upward andit is noted that the trend lines, with and without the agent, areroughly parallel, and about 15 barrels apart. Constant pumpingconditions were maintained throughout this experiment and the reason forthe sharp peaks on the eighth and tenth days is not known.

In the second experiment, illustrated by the curves of Fig. 2, the sameagent was introduced into the same well at a period, some months later,during which the trend of productivity was downward. The addition wasmade in two periods of twenty and twenty-one days respectively with athirteen day interval between them. The dosage during the first periodaveraged twenty-five millilitres per day, during the second periodthirty millilitres or approximately one fluid ounce. The production ofthe well responded sharply when the feed of the agent began and fell offsomewhat more slowly when it was discontinued. As before, the trendlines with and without the agent are roughly parallel, but are separatedby a greater distance, equal to about thirty barrels per day.

The quantities of these agents required to produce a material increasein production is extremely minute, of the order of one-half part permillion to five parts per million and more commonly about 1 part to twoparts per million. This is in sharp contrast to the behavior of the sameand similar bodies in lubricating oils, in which the common usage isfrom fifty to five hundred parts per million. Consumptions of thislarger order would. of course, be entirely out of the questioneconomically in the production of crude petroleum, butthe quantitiesactually required ordinarily cost less than one cent per barrel whenfigured on the total production of the well or from two to three centsper barrel when figured only on the increased production gained by theiruse.

In order to obtain increased production with the use of these minutedosages of the defoamant it is essential to dilute the actual agent verystrongly, as for example with from two hundred to five hundred times itsvolumes of a suitable solvent such as kerosene or diesel oil. When sodiluted the agent may be fed into the well casing, outside the tubing,either in slugs at intervals or in a very fine stream by the use of anyproportioning device.

The well in which this destabilizing agent was used is provided with amoderately effective gas anchor, which was operative during the entireterm of both experiments. It is believed (though not demonstrated withcertainty) that the remarkable increase in production resulting from theaddition of these minute quantities of the agent was due in large partto the efiect of the agent in increasing the effectiveness of the anchorrather than to the resolution of froth in the well casing.

A gas anchor has two functions, the relative values of which vary withthe quantitative relation between gas and oil in the well fluid. First,the anchor provides a long and more or less vertical passage throughwhich the fluid moves downwardly at such low velocity that at least thelarger gas bubbles may move upwardly through it at a greater velocityand thus escape being drawn into the pump suction. This is a separatingfunction purely, and is most effective when the gas bubbles arerelatively large and are free to move through a relatively largeproportion of liquid oil.

The anchor also provides extended metallic surfaces over which the wellfluid moves and which tend to rupture the oil skins surrounding the gasbubbles and to aggregate them to bubbles of greater dimensions whichrise and separate from the oil with greater rapidity. This resolvingfunction becomes of major importance when a true froth is entering theanchor, that is to say, when the gas bubbles are separated only by thinoil skins. In such cases, which are common in the production of gassy,viscous oils, even a slight decrease in the stability of the froth leadsto extreme magnification of the resolving eifcct of the anchor and ofits effectiveness in feeding only liquid oil to the standing valve ofthe pump.

We claim as our invention: 7

1. In the operation of an oil well having a pump and tubing throughwhich oil is, pumped, the step of introducing a minute quantity of adihydrocarbon silicone into the space within the well surrounding thetubing, whereby the productivity of said well is increased, the quantityof said silicone so introduced being from one-half part per million tofive parts per million figured on the net volume of oil produced by saidwell.

2. In the operation of an oil well having a pump and tubing throughwhich oil is pumped, the

step of introducing a minute quantity of dimethyl silicone into thespace within the well surrounding the tubing, whereby the productivityof said well is increased, the quantity of said silicone so REFERENCESCITED The following references are of record in the file of this patent;

UNITED STATES PATENTS Number Name 4 Date 2,258,218 Rochow Oct. '1. 19412,368,346 Coberly Jan. 30, 1945 15 2,384,384 McGregor Sept. 4, 1945

1. IN THE OPERATION OF AN OIL WELL HAVING A PUMP AND TUBING THROUGHWHICH OIL IS PUMPED, THE STEP OF INTRODUCING A MINUTE QUANTITY OF ADIHYDROCARBON SILICONE INTO THE SPACE WITHIN THE WELL SURROUNDING THETUBING THE SPACE WITHIN THE WELL SURSAID WELL IS INCREASED, THE QUANTITYOF SAID SILICONE SO INTRODUCED BEING FROM ONE-HALF PART PER MILLION TOFIVE PARTS PER MILLION FIGURED ON THE NET VOLUME OF OIL PRODUCED BY SAIDWELL.